The present invention relates to a device for circulating developer for use with an image forming apparatus such as a copying machine, facsimile apparatus or the like, which conveys developer from a cleaning device into a developing device for reuse.
It is generally known that in an image forming apparatus such as a copying machine, residual developer remained on a photosensitive drum after image transfer operation is removed and recovered with a cleaning device. To reuse recovered developer, a developer circulating device for conveying developer from a cleaning device into a developing device has been used.
FIG. 11 shows a prior art device of this type having a developing device 102 and a cleaning device 103 both mounted around a photosensitive drum 101, and a circulating passage 104 which is provided between the developing device 102 and the cleaning device 103 so as to communicate with both devices. The cleaning device 103 accommodates a discharging screw 107 by which developer is discharged to the circulating passage 104 from the cleaning device 108.
The circulating passage 104 has a wall 104a at its terminal end. Beneath the wall 104a is provided an opening 102a as an entrance to the developing device 102. A supplying screw 105 for supplying developer through the opening 102a into the developing device 102 extends transversely of the developing device 102. The supplying screw 105 is formed into a spiral extending in a direction throughout the length thereof. Rotation of the supplying screw 105 supplies developer from a side of the developing device 102 into the developing device 102.
The circulating passage 104 has a spiral conveying member 106 placed therein and extending to the terminal end thereof. The conveying member 106 is rotated so that developer is conveyed from the cleaning device 103 to the developing device 102. The supplying screw 105, the conveying member 106, and the discharging screw 107 are interrelatedly driven synchronously with a main motor.
The problem arising in this prior art circulating device are as follows:
(1) All the developer conveyed by the conveying member 106 to the terminal end of the circulating passage 104 is not always supplied through the opening 102a into the developing device 102. When the fluidity of developer lowers, for instance, due to a high humidity, developer is liable to adhere to the surface of the conveying member 106 and be conveyed onto the wall 104a without flowing into the opening 102a. Consequently, developer is deposited in the terminal portion of the conveying member 106 with being pressed continuously against the wall 104a. This causes the conveying member 106 to inadvertently stop rotating and the drive of the conveying member 106 is liable to come into a lock state.
(2) In the prior art device, the supplying screw 105 is driven together with the conveying member 106 and the discharging screw 107 during the operation of the main motor or of the photosensitive drum 101. This causes excessive agitation of toner in the developing device 102 which results in deformation and blocking of toner particles.
It has been seen that this problem can be solved by controlling the supplying screw 105, the conveying member 106, the discharging screw 107, and a toner supply device for supplying used toner into the developing device 102 in accordance with the density of toner in the developing device, as disclosed in Unexamined Patent Publication No.133480/1985. However, in the device, the discharging screw 107 is driven only when toner is fed. Since toner in the cleaning device 103 is recovered and discharged only during the supply of toner, toner is liable to be left in the cleaning device 103 and be deposited on a lower blade for closing a clearance between the photosensitive drum 101 and the cleaning device 103. Consequently, the lower blade is pressed downward by the deposited toner, which produces an undesirable space between the photosensitive drum 101 and the cleaning device 103. In addition, a further problem occurs which residual toner is liable to produce blocks of toner in the cleaning device 103.
(3) As the supplying screw 105 is formed into the aforesaid spiral extending in one direction throughout the length thereof, developer supplied into the developing device 102 is conveyed in only one direction toward the downstream portion of the supplying screw 106 or a furthermost portion of the developing device 102. This allows developer to be supplied unevenly to the furthermost portion of the developing device 102, which results in a reduced storage efficiency. When developer is conveyed in only one direction, it is pressed against the furthermost wall of the developing device 102 and deposited in the downstream portion of the supplying screw 105 to cause the supplying screw 105 to come into a lock state.
(4) Unused developer contained in the developing device 102 prior to an initial operation is required to contain in an airtight condition to prevent it from deterioration. It is difficult in the prior art device to keep unused developer completely in an airtight condition as the developing device 102 and the cleaning device 103 are communicated with each other by the circulating passage 104. In particular, when the developing device 102 and the cleaning device 103 tilt during transportion, there is a likelihood that a portion of unused developer may flow through the circulating passage 104 into the cleaning device 103.